Pickups and small trucks are widely used for carrying loose particulate matter such as gravel, mulch, leaves, and the like. Such vehicles have a solid floor and solid sides, that is, sides which contain no holes. A solid floor and sides is absolutely required when hauling such loads. Otherwise, some of the particulate matter will be lost through holes or voids in a floor or sidewall.
Also common in the art are trailers which allow a user to carry a large load without dedicating a vehicle to that load. For instance, suppose an individual wants to haul a large amount of gravel to his home but wants to unload the gravel at a more convenient time. Rather than hauling the gravel in a pickup, he chooses to pull a trailer behind his pickup, carry the gravel home in the trailer and unload it on a later date. However, there is a problem. The trailer has a solid floor but only has a safety frame around three sides. In order to carry a large amount of gravel, side walls must be built and attached around the frame.